Make Counter and MinMaxSumCount aggregators thread safe #439

mauriciovasquezbernal · 2020-02-21T16:37:52Z

The update() and the take_checkpoint() functions on these aggregators can be called concurrently, update() is called from the user context while take_checkpoint() is invoked from the controller. It is also possible to receive concurrent calls to the update() function from the user. For these reasons this PR adds a locking mechanism to guarantee that those functions are thread safe. This PR also implements some concurrency tests for those aggregators.

As a note, it could be a temporal solution as in the future we want to explore atomic to avoid the cost of locking.

It's possible tha future.running() returns BEFORE the task is scheduled.

codecov-io · 2020-02-21T19:35:13Z

Codecov Report

Merging #439 into master will increase coverage by 0.31%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #439      +/-   ##
==========================================
+ Coverage   88.25%   88.56%   +0.31%     
==========================================
  Files          41       41              
  Lines        2078     2082       +4     
  Branches      238      238              
==========================================
+ Hits         1834     1844      +10     
+ Misses        172      169       -3     
+ Partials       72       69       -3

Impacted Files	Coverage Δ
.../src/opentelemetry/sdk/metrics/export/aggregate.py	`100% <100%> (+11.53%)`	⬆️
...app/src/opentelemetry_example_app/flask_example.py	`100% <0%> (ø)`	⬆️
...emetry-sdk/src/opentelemetry/sdk/trace/__init__.py	`91.2% <0%> (ø)`	⬆️

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c24t

One comment about a missing lock, and a few other minor comments, but otherwise this looks great.

Also very nice that the concurrency tests fail if you remove the locks.

c24t · 2020-02-21T20:26:08Z

opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/aggregate.py

-        self.current = 0
+        with self._lock:
+            self.checkpoint = self.current
+            self.current = 0

    def merge(self, other):
        self.checkpoint += other.checkpoint


Don't you need to lock here too?

According to my understanding merge() and take_checkpoint() will be never called concurrently. Those methods are invoked in Batcher::process() that is invoked from Meter::collect() that is never concurrent. @lzchen could you please check this reasoning?

opentelemetry-python/opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/batcher.py

Lines 87 to 103 in ed25287

def process(self, record):

# Checkpoints the current aggregator value to be collected for export

record.aggregator.take_checkpoint()

batch_key = (record.metric, record.label_set)

batch_value = self._batch_map.get(batch_key)

aggregator = record.aggregator

if batch_value:

# Update the stored checkpointed value if exists. The call to merge

# here combines only identical records (same key).

batch_value.merge(aggregator)

return

if self.stateful:

# if stateful batcher, create a copy of the aggregator and update

# it with the current checkpointed value for long-term storage

aggregator = self.aggregator_for(record.metric.__class__)

aggregator.merge(record.aggregator)

self._batch_map[batch_key] = aggregator

Even still, I think it's better not to rely on the behavior of the caller here. Even better: if they're never called concurrently, there will never be lock contention to slow this down.

I agree, I added locks to merge too but I didn't added tests for that. We can revisit this later on when considering the use of atomics libraries here.

c24t · 2020-02-21T20:35:16Z

opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/aggregate.py

@@ -63,46 +67,45 @@ class MinMaxSumCountAggregator(Aggregator):
    """Agregator for Measure metrics that keeps min, max, sum and count."""

    _TYPE = namedtuple("minmaxsumcount", "min max sum count")
+    _EMPTY = _TYPE(None, None, None, 0)


Shouldn't sum be 0 too?

Good question, I don't have a strong feeling about that, if you have please let me know and I'll change it.

I think it should be because of https://en.wikipedia.org/wiki/Identity_element, also not a strong opinion.

Given that, min should be inf and max -inf. The point is, do we want to have a special value to indicate that it hasn't been computed?. i.e, None. I don't have a strong opinion, the go implementation returns an error in such case, even if I don't understand the details of the race condition that is mentioned there.

https://github.com/open-telemetry/opentelemetry-go/blob/29cd0c08b70052860d9a6ce0510e102537ff7fa7/sdk/metric/aggregator/minmaxsumcount/mmsc.go#L81-L86

Either way's fine with me, but I'd expect sum and count to either both be None or both be 0. As for +/-inf I think the min/max of an empty set is literally undefined, but the sum and count are defined and 0.

But this is getting dangerously close to philosophy. LGTM as is.

opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/aggregate.py

c24t · 2020-02-21T21:03:15Z

opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/aggregate.py

-            self._max(self.checkpoint.max, other.checkpoint.max),
-            self._sum(self.checkpoint.sum, other.checkpoint.sum),
-            self.checkpoint.count + other.checkpoint.count,
+        self.checkpoint = self._merge_checkpoint(


I think you still need to lock here:

thread 1 calls merge, loads self.checkpoint

thread 2 calls take_checkpoint, updates self.checkpoint

thread 1 updates self.checkpoint by merging the value it loaded in step 1, undoing step 2

This is based on:

In [9]: dis.dis(MinMaxSumCountAggregator.merge) 109 0 LOAD_FAST 0 (self) 2 LOAD_METHOD 0 (_merge_checkpoint) 110 4 LOAD_FAST 0 (self) 6 LOAD_ATTR 1 (checkpoint) 8 LOAD_FAST 1 (other) << thread 2 start 10 LOAD_ATTR 1 (checkpoint) 12 CALL_METHOD 2 14 LOAD_FAST 0 (self) 16 STORE_ATTR 1 (checkpoint) 18 LOAD_CONST 0 (None) 20 RETURN_VALUE In [10]: dis.dis(MinMaxSumCountAggregator.take_checkpoint) 104 0 LOAD_FAST 0 (self) 2 LOAD_ATTR 0 (_lock) 4 SETUP_WITH 22 (to 28) 6 POP_TOP 105 8 LOAD_FAST 0 (self) 10 LOAD_ATTR 1 (current) 12 LOAD_FAST 0 (self) 14 STORE_ATTR 2 (checkpoint) 106 16 LOAD_FAST 0 (self) << thread 1 overwrite 18 LOAD_ATTR 3 (_EMPTY) 20 LOAD_FAST 0 (self) 22 STORE_ATTR 1 (current) 24 POP_BLOCK 26 LOAD_CONST 0 (None) >> 28 WITH_CLEANUP_START 30 WITH_CLEANUP_FINISH 32 END_FINALLY 34 LOAD_CONST 0 (None) 36 RETURN_VALUE

Please see #439 (comment).

opentelemetry-sdk/tests/metrics/export/test_export.py

opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/aggregate.py

c24t

LGTM after addressing @ocelotl's comments.

c24t · 2020-02-25T07:58:18Z

opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/aggregate.py

-        self.current = 0
+        with self._lock:
+            self.checkpoint = self.current
+            self.current = 0

    def merge(self, other):
        self.checkpoint += other.checkpoint


Even still, I think it's better not to rely on the behavior of the caller here. Even better: if they're never called concurrently, there will never be lock contention to slow this down.

c24t · 2020-02-25T07:59:21Z

opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/aggregate.py

@@ -63,46 +67,45 @@ class MinMaxSumCountAggregator(Aggregator):
    """Agregator for Measure metrics that keeps min, max, sum and count."""

    _TYPE = namedtuple("minmaxsumcount", "min max sum count")
+    _EMPTY = _TYPE(None, None, None, 0)


I think it should be because of https://en.wikipedia.org/wiki/Identity_element, also not a strong opinion.

Rename TracerSource to TracerProvider (open-telemetry#441) Following discussion in open-telemetry#434, align the name with the specification. Co-authored-by: Chris Kleinknecht <libc@google.com> Fix new ext READMEs (open-telemetry#444) Some of the new ext packages had ReStructuredText errors. PyPI rejected the uploads for these packages with: HTTPError: 400 Client Error: The description failed to render for 'text/x-rst'. See https://pypi.org/help/#description-content-type for more information. for url: https://upload.pypi.org/legacy/ Adding attach/detach methods as per spec (open-telemetry#429) This change updates the Context API with the following: - removes the remove_value method - removes the set_current method - adds attach and detach methods Fixes open-telemetry#420 Co-authored-by: Chris Kleinknecht <libc@google.com> Make Counter and MinMaxSumCount aggregators thread safe (open-telemetry#439) OT Collector trace exporter (open-telemetry#405) Based on the OpenCensus agent exporter. Fixes open-telemetry#343 Co-authored-by: Chris Kleinknecht <libc@google.com> API: Renaming TraceOptions to TraceFlags (open-telemetry#450) Renaming TraceOptions to TraceFlags, which is the term used to describe the flags associated with the trace in the OpenTelemetry specification. Closes open-telemetry#434 api: Implement "named" meters + Remove "Batcher" from Meter constructor (open-telemetry#431) Implements open-telemetry#221. Also fixes open-telemetry#394. Stateful.py and stateless.py in metrics example folder are not changed to use the new loader in anticipation of open-telemetry#422 being merged first and removing them. Lastly, moves InstrumentationInfo from trace.py in the sdk to utils. Prepare to host on readthedocs.org (open-telemetry#452) sdk: Implement observer instrument (open-telemetry#425) Observer instruments are used to capture a current set of values at a point in time [1]. This commit extends the Meter interface to allow to register an observer instrument by pasing a callback that will be executed at collection time. The logic inside collection is updated to consider these instruments and a new ObserverAggregator is implemented. [1] https://github.com/open-telemetry/opentelemetry-specification/blob/master/specification/api-metrics.md#observer-instruments sdk: fix ConsoleSpanExporter (open-telemetry#455) 19d573a ("Add io and formatter options to console exporter (open-telemetry#412)") changed the way spans are printed by using write() instead of print(). In Python 3.x sys.stdout is line-buffered, so the spans were not being printed to the console at the right timing. This commit fixes that by adding an explicit flush() call at the end of the export function , it also changes the default formatter to include a line break. To be precise, only one of the changes was needed to solve the problem, but as a matter of completness both are included, i.e, to handle the case where the formatter chosen by the user doesn't append a line break. jaeger: Usage README Update for opentelemetry-ext-jaeger (open-telemetry#459) Usage docs for opentelemetry-ext-jaeger need to be updated after the change to `TracerSource` with v0.4. Looks like it was partially updated already. Users following the usage docs will currently run into this error: `AttributeError: 'Tracer' object has no attribute 'add_span_processor'` api: Implementing Propagators API to use Context (open-telemetry#446) Implementing Propagators API to use Context. Moving tracecontexthttptextformat to trace/propagation, as TraceContext is specific to trace rather that broader context propagation. Using attach/detach for wsgi and flask extensions, enabling activation of the full context rather that activating of a sub component such as traces. Adding a composite propagator. Co-authored-by: Mauricio Vásquez <mauricio@kinvolk.io>

Total Changelog: Documentations has been significantly overhauled, including: * a getting started guide * examples has been consolidated to an docs/examples folder * several minor improvements to the examples in each extension's readme. - Adding Correlation Context API and propagator ([open-telemetry#471](open-telemetry#471)) - Adding a global configuration module to simplify setting and getting globals ([open-telemetry#466](open-telemetry#466)) - Rename metric handle to bound metric ([open-telemetry#470](open-telemetry#470)) - Moving resources to sdk ([open-telemetry#464](open-telemetry#464)) - Implementing propagators to API to use context ([open-telemetry#446](open-telemetry#446)) - Implement observer instrument for metrics ([open-telemetry#425](open-telemetry#425)) - Adding named meters, removing batchers ([open-telemetry#431](open-telemetry#431)) - Renaming TraceOptions to TraceFlags ([open-telemetry#450](open-telemetry#450)) - Renaming TracerSource to TraceProvider ([open-telemetry#441](open-telemetry#441)) - Adding Correlation Context SDK and propagator ([open-telemetry#471](open-telemetry#471)) - Adding OT Collector metrics exporter ([open-telemetry#454](open-telemetry#454)) - Improve validation of attributes ([open-telemetry#460](open-telemetry#460)) - Re-raise errors caught in opentelemetry.sdk.trace.Tracer.use_span() (open-telemetry#469) ([open-telemetry#469](open-telemetry#469)) - Adding named meters, removing batchers ([open-telemetry#431](open-telemetry#431)) - Make counter and MinMaxSumCount aggregators thread safe ([open-telemetry#439](open-telemetry#439)) - Initial release. Support is included for both trace and metrics.

Rename TracerSource to TracerProvider (open-telemetry#441) Following discussion in open-telemetry#434, align the name with the specification. Co-authored-by: Chris Kleinknecht <libc@google.com> Fix new ext READMEs (open-telemetry#444) Some of the new ext packages had ReStructuredText errors. PyPI rejected the uploads for these packages with: HTTPError: 400 Client Error: The description failed to render for 'text/x-rst'. See https://pypi.org/help/#description-content-type for more information. for url: https://upload.pypi.org/legacy/ Adding attach/detach methods as per spec (open-telemetry#429) This change updates the Context API with the following: - removes the remove_value method - removes the set_current method - adds attach and detach methods Fixes open-telemetry#420 Co-authored-by: Chris Kleinknecht <libc@google.com> Make Counter and MinMaxSumCount aggregators thread safe (open-telemetry#439) OT Collector trace exporter (open-telemetry#405) Based on the OpenCensus agent exporter. Fixes open-telemetry#343 Co-authored-by: Chris Kleinknecht <libc@google.com> API: Renaming TraceOptions to TraceFlags (open-telemetry#450) Renaming TraceOptions to TraceFlags, which is the term used to describe the flags associated with the trace in the OpenTelemetry specification. Closes open-telemetry#434 api: Implement "named" meters + Remove "Batcher" from Meter constructor (open-telemetry#431) Implements open-telemetry#221. Also fixes open-telemetry#394. Stateful.py and stateless.py in metrics example folder are not changed to use the new loader in anticipation of open-telemetry#422 being merged first and removing them. Lastly, moves InstrumentationInfo from trace.py in the sdk to utils. Prepare to host on readthedocs.org (open-telemetry#452) sdk: Implement observer instrument (open-telemetry#425) Observer instruments are used to capture a current set of values at a point in time [1]. This commit extends the Meter interface to allow to register an observer instrument by pasing a callback that will be executed at collection time. The logic inside collection is updated to consider these instruments and a new ObserverAggregator is implemented. [1] https://github.com/open-telemetry/opentelemetry-specification/blob/master/specification/api-metrics.md#observer-instruments sdk: fix ConsoleSpanExporter (open-telemetry#455) 19d573a ("Add io and formatter options to console exporter (open-telemetry#412)") changed the way spans are printed by using write() instead of print(). In Python 3.x sys.stdout is line-buffered, so the spans were not being printed to the console at the right timing. This commit fixes that by adding an explicit flush() call at the end of the export function , it also changes the default formatter to include a line break. To be precise, only one of the changes was needed to solve the problem, but as a matter of completness both are included, i.e, to handle the case where the formatter chosen by the user doesn't append a line break. jaeger: Usage README Update for opentelemetry-ext-jaeger (open-telemetry#459) Usage docs for opentelemetry-ext-jaeger need to be updated after the change to `TracerSource` with v0.4. Looks like it was partially updated already. Users following the usage docs will currently run into this error: `AttributeError: 'Tracer' object has no attribute 'add_span_processor'` api: Implementing Propagators API to use Context (open-telemetry#446) Implementing Propagators API to use Context. Moving tracecontexthttptextformat to trace/propagation, as TraceContext is specific to trace rather that broader context propagation. Using attach/detach for wsgi and flask extensions, enabling activation of the full context rather that activating of a sub component such as traces. Adding a composite propagator. Co-authored-by: Mauricio Vásquez <mauricio@kinvolk.io>

* chore: cleanup closed issues * chore: update basic tracer * chore: clear open-telemetry#59 * chore: clear todo in DEFAULT_CONFIG

mauriciovasquezbernal added 2 commits February 21, 2020 11:10

sdk/metrics/aggregators: make Counter threadsafe

6e6f6db

sdk/metrics/aggregator: make MinMaxSumCount threadsafe

1f9444e

mauriciovasquezbernal added the metrics label Feb 21, 2020

mauriciovasquezbernal requested a review from a team February 21, 2020 16:37

use future.done() instead of future.running()

2482e09

It's possible tha future.running() returns BEFORE the task is scheduled.

c24t reviewed Feb 21, 2020

View reviewed changes

use float("inf") instead of 2 ** 32.

80d73ab

ocelotl suggested changes Feb 24, 2020

View reviewed changes

opentelemetry-sdk/tests/metrics/export/test_export.py Outdated Show resolved Hide resolved

opentelemetry-sdk/src/opentelemetry/sdk/metrics/export/aggregate.py Show resolved Hide resolved

use staticmethod instead of classmethod

e9580d8

c24t approved these changes Feb 25, 2020

View reviewed changes

add locks on merge() too

53ae9ae

ocelotl approved these changes Feb 27, 2020

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c24t merged commit 2578b37 into open-telemetry:master Feb 27, 2020

toumorokoshi mentioned this pull request Mar 16, 2020

Changelog and version updates for 0.5b0 release #498

Merged

mauriciovasquezbernal deleted the mauricio/add-aggregator-locks branch April 14, 2020 21:50

srikanthccv pushed a commit to srikanthccv/opentelemetry-python that referenced this pull request Nov 1, 2020

chore: TODO cleanup (open-telemetry#439)

d3ce25c

* chore: cleanup closed issues * chore: update basic tracer * chore: clear open-telemetry#59 * chore: clear todo in DEFAULT_CONFIG

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Make Counter and MinMaxSumCount aggregators thread safe #439

Make Counter and MinMaxSumCount aggregators thread safe #439

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codecov-io commented Feb 21, 2020 •

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	def process(self, record):
	# Checkpoints the current aggregator value to be collected for export
	record.aggregator.take_checkpoint()
	batch_key = (record.metric, record.label_set)
	batch_value = self._batch_map.get(batch_key)
	aggregator = record.aggregator
	if batch_value:
	# Update the stored checkpointed value if exists. The call to merge
	# here combines only identical records (same key).
	batch_value.merge(aggregator)
	return
	if self.stateful:
	# if stateful batcher, create a copy of the aggregator and update
	# it with the current checkpointed value for long-term storage
	aggregator = self.aggregator_for(record.metric.__class__)
	aggregator.merge(record.aggregator)
	self._batch_map[batch_key] = aggregator

Make Counter and MinMaxSumCount aggregators thread safe #439

Make Counter and MinMaxSumCount aggregators thread safe #439

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codecov-io commented Feb 21, 2020 •

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